Optical detection system for improved alignment

ABSTRACT

Optical detection system having: an emitter providing a collimated light beam; a receiver receiving the collimated light beam, the receiver having: a receiver lens converging the collimated light beam along an optical axis, and a corner reflector, the corner reflector having three planar surfaces perpendicular to each other and a symmetry axis coinciding with an intersection point of the three planar surfaces and forming an equal angle with each of the planar surfaces, the corner reflector reflecting the collimated light beam about the symmetry axis. The optical axis of the receiver lens is parallel to the symmetry axis of the corner reflector.

TECHNICAL FIELD

This disclosure relates to optical detection systems comprising anemitter and a receiver. This disclosure also relates to a method foraligning an emitter and a receiver of an optical detection system

BACKGROUND ART

Optical detection systems rely on the properties of light to detectobjects. Optical detection systems typically include an emitter, forproviding light, and a receptor, for receiving light. When lightprovided by the emitter is interrupted or reflected by an object, theamount of light arriving at the receiver changes. The receiver detectsthe change and converts it to an electrical output.

An optical detection system may for example be a through-beam sensor.The emitter of the through-beam sensor aims a light beam directlytowards the receiver. When an object interrupts the light beamtravelling between the emitter and the receiver, the receiver'selectrical output changes.

Through-beam sensors enable long distance sensing, as the receiver canbe placed far away from the emitter. However, accurate detection relieson proper alignment of the receiver with the emitter to ensure that thelight beam is received.

Classically, proper alignment is achieved by iteratively adjusting thepositions of the emitter and the receiver. However, such an iterativeprocess may be time consuming. For each iteration, it may be unclearwhich of the emitter or the receiver is misaligned, potentially leadingto further misalignments. When the emitter and receiver are separated bylarge distances, such as over 10 m, an operator would be required torepeatedly travel back and forth.

An object of the present disclosure is to propose an optical detectionsystem which enables simple and quick alignment of the emitter and thereceiver, without introducing additional cost or complexity to theoptical detection system.

SUMMARY

It is proposed an optical detection system comprising:

-   -   an emitter configured to provide a collimated light beam;    -   a receiver configured to receive the collimated light beam, the        receiver comprising:        -   a receiver lens having an optical axis, the receiver lens            adapted to converge the collimated light beam along the            optical axis, and        -   at least one corner reflector, said at least one corner            reflector comprising three planar surfaces perpendicular to            each other and a symmetry axis coinciding with an            intersection point of the three planar surfaces, said            symmetry axis forming an equal angle with each of the planar            surfaces, said at least one corner reflector adapted to            reflect the collimated light beam about the symmetry axis,            wherein the optical axis of the receiver lens is parallel to            the symmetry axis of said at least one corner reflector.

The following features, can be optionally implemented, separately or incombination one with the others:

-   -   the receiver lens and the at least one corner reflector are in        one piece;    -   the collimated light beam is within the visible spectrum or        within the infrared spectrum;    -   the receiver comprises a plurality of corner reflectors forming        an array, and the array is preferably a line or a square;    -   the receiver comprises a first corner reflector and a second        corner reflector aligned with the first corner reflector;    -   the collimated light beam converges at a focal point of the        receiver lens, and the receiver comprises a photodiode        positioned at the focal point of the receiver lens;    -   the receiver further comprises an indicator configured to        indicate whether collimated light is received by the photodiode;    -   the at least one corner reflector extend on a side of the        receiver comprising the photodiode;    -   the receiver lens and each corner reflector are made of        optically transparent material, preferably the receiver lens and        each corner reflector are made of polycarbonate, polymethyl        methacrylate (PMMA), a cyclo olefin polymer (COP) or glass;    -   the emitter comprises an LED and an emitter lens, and the LED is        positioned at a focal point of the emitter lens to provide the        collimated light beam;    -   the LED is pulse modulated;    -   the emitter comprises a first housing and the receiver comprises        a second housing, distinct from the first housing;    -   the emitter and the receiver are around 15 m apart.

In another aspect, it is proposed a method for aligning an opticaldetection system according to any of the preceding claims, wherein themethod comprises:

-   -   providing, by the emitter, the collimated light beam;    -   adjusting the position of the emitter to obtain a reflected        collimated light beam at the emitter;    -   following adjustment of the emitter, adjusting the position of        the receiver to align the collimated light beam with the optical        axis of the receiver lens.

BRIEF DESCRIPTION OF DRAWINGS

Other features, details and advantages will be shown in the followingdetailed description and on the figures, on which:

FIG. 1 schematically illustrates a cross sectional view of an opticaldetection system according to an embodiment.

FIG. 2 illustrates a detail of FIG. 1.

FIG. 3 illustrates an alternative embodiment of FIG. 2.

FIG. 4 illustrates a perspective view of an optical part that can beimplemented into the optical detection system of FIG. 1 according to anembodiment.

FIG. 5 illustrates a back view of the optical part of FIG. 4.

FIG. 6 illustrates an example of an array that can be implemented in theoptical part of FIG. 3 according to an embodiment.

FIG. 7 illustrates an example of a result of the optical detectionsystem of FIG. 1.

FIG. 8 illustrates a method for aligning the components of the opticaldetection system of FIG. 1.

FIG. 9A illustrates the components of the optical detection system ofFIG. 1 in a first position.

FIG. 9B illustrates the components of the optical detection system ofFIG. 1 in a second position.

FIG. 9C illustrates the components of the optical detection system ofFIG. 1 in a third position.

DESCRIPTION OF EMBODIMENTS

FIG. 1 illustrates an optical detection system 10 comprising an emitter12 and a receiver 14. The emitter 12 provides a collimated light beam16. The receiver 14 is configured to receive the collimated light beam16 provided by the emitter 12. The emitter and the receiver aredistanced from one another to detect objects interrupting the collimatedlight beam 16 travelling from the emitter 12 to the receiver 14.

The emitter 12 essentially comprises a light-emitting diode (LED) 18 andan emitter lens 20.

The LED 18 is connected to an electronic circuit to receive an electriccurrent. The LED 18 converts the electric current into light. The LED 18may be pulse modulated, and may emit light repeatedly at fixedintervals. Such modulation may improve the removal of lightinterferences arising between the emitter 12 and the receiver 14.

Here, the LED 18 provides light within the visible spectrum. By visiblespectrum, it is to be understood that the light provided has a wavelength between 380 and 700 nm. An operator may therefore see thecollimated light beam 16. Alternatively, the LED 18 could provide lightwithin the infrared (IR) spectrum, to be detected by a photoreceptor.The LED 18 could also provide light in the ultra violet (UV) domain.

The emitter lens 20 is a converging lens 20 having an optical axis X_(e)and a focal point F_(e) coincident with the optical axis X_(e). The LED18 is positioned at the focal point F_(e) of the emitter lens 20. Lightprovided by the LED 18 at the focal point F_(e) exits the emitter lens20 collimated parallel to the optical axis X_(e). The collimated lightbeam 16 may be directed towards the receiver 14.

It should be noted that the collimated light beam 16 diverges as itmoves away from the emitter lens 20. An angle of divergence θ_(E) of thecollimated light beam 16 may be around 1.2°. The angle of divergenceθ_(E) causes a spread of the collimated light beam 16 measured from theoptical axis X_(e). A radius r of the collimated light beam 16 increaseswith distance away from the emitter lens 20.

Here, the emitter lens 20 has a flat face 22 and a convex surface 24protruding from the flat face 22. The flat face 22 is oriented towardsthe LED 18, and the convex surface 24 is oriented towards the outside ofthe emitter 12. In other examples, the flat face 22 may be orientedtowards the outside of the emitter 12 and the convex surface 24 may beoriented towards the LED 18. In yet another example, the emitter lens 20may have two convex surfaces.

The emitter 12 may optionally comprise a second converging lens 26 alsohaving an optical axis A_(E) and a focal point C_(E). A photoreceptor 27may be positioned at the focal point C_(E) of the second converging lens26. Thus, light rays arriving at the second converging lens 26 parallelto the optical axis A_(E) converge at the focal point C_(E) to bedetected by the photoreceptor 27.

In the example illustrated in FIG. 1, the second converging lens 26 ispositioned vertically below the emitter lens 20. The optical axis A_(E)of the second converging lens 26 is parallel to the optical axis X_(E)of the emitter lens 20. The emitter 12 can therefore be used as areflective sensor. In addition, the second converging lens 26 may detectthe collimated light beam 16 reflected by the receiver 14 toautomatically determine whether the receiver 14 is aligned with theemitter 12.

The second converging lens 26 may be in one piece with the emitter lens20 to form a single emitter optical part. The emitter optical partinsures alignment of the optical axis X_(E) of the emitter lens 20 andthe optical axis A_(E) of the second converging lens 26. Alternatively,the emitter lens 20 and the second converging lens 26 can be in twoseparate parts.

The emitter lens 20, and the second converging lens 26 if applicable, ismade of optically transparent material. The optically transparentmaterial may be plastic, preferably polycarbonate, polymethylmethacrylate (PMMA) or a cyclo olefin polymer (COP), or glass.

The emitter lens 20, the LED 18, the second converging lens 26 andphotoreceptor 27 if applicable, and electronic components used forpowering, operation and control of the emitter 12 are received in afirst housing 28. The first housing 28 may be fixed to a structuralelement to secure position of the emitter 12.

In the illustrated example, the first housing 28 has a cylindricalshape. The optical axis X_(e) of the converging lens 20 and, ifapplicable, the optical axis A_(E) of the second converging lens 26 maybe parallel to a longitudinal axis of the first housing 28.Alternatively, the first housing 28 could be rectangular or any othershape.

The receiver 14 essentially comprises a receiver lens 30, aphotoreceptor 32 and at least one corner reflector 34.

The receiver lens 30 is also a converging lens 30 having an optical axisX_(R) and a focal point F_(R) coinciding with the optical axis X_(R).The photoreceptor 32 is positioned at the focal point F_(R) of thereceiver lens 30. The collimated light beam 16 arriving at the receiverlens 30 parallel to the optical axis X_(R) converges at the focal pointF_(R) of the receiver lens 30 to be detected by the photoreceptor 32.

In an example shown in FIG. 2, the receiver lens 30 has a flat face 36and a convex surface 38 protruding from the flat face 36. The flat face36 is oriented towards the photoreceptor 32 and the convex surface 38faces towards the outside of the receiver 14. In another example shownin FIG. 3, the flat face 36 is oriented towards the outside of thereceiver 14 and the convex surface 38 faces towards the photoreceptor32.

The photoreceptor 32 converts the converged collimated light beam 16into an electrical output. Further electronic components may amplify andprocess the electrical output to determine whether an object hasinterfered with the collimated light beam 16 travelling between theemitter 12 and the receiver 14.

The at least one corner reflector 34 is arranged close to the receiverlens 30. The receiver lens 30 and each corner reflector 34 both receivethe collimated light beam 16 provided by the emitter 12. In theillustrated examples, the one or more corner reflectors 34 arepositioned vertically below the receiver lens 30. However, the one ormore corner reflectors 34 could be positioned at any position around thereceiver lens 30.

Each corner reflector 34 has three planar surfaces 40 a, 40 b, 40 cperpendicular to each other. Each corner reflector 34 has a symmetryaxis A coinciding with an intersection point of the three planarsurfaces 40 a, 40 b, 40 c and forming an equal angle with each of theplanar surfaces 40 a, 40 b, 40 c. The collimated light beam 16 arrivingat each corner reflector 34 is reflected about the symmetry axis A. Areflected collimated light beam 42 is obtained even if the collimatedlight beam 16 does not arrive parallel to the symmetry axis A of eachcorner reflector 34. The reflected collimated light beam 42 indicatesthat the receiver 14 is within the radius r of the collimated light beam16.

The symmetry axis A of each corner reflector 34 is parallel to theoptical axis X_(R) of the receiver lens 30. In other words, each of thethree planar surfaces 40 a, 40 b, 40 c of each corner reflector 34 formsan equal angle with the flat face 36 of the receiver lens 30. Thereflected collimated light beam 42 may be observed at the emitter 12, asshown in FIG. 7. The position of the emitter 12 may be adjusted untilthe reflected collimated light beam 42 is observed at the emitter 12.

Here, each corner reflector 34 is a solid cube corner. Each cornerreflector 34 is a cube of solid material. However, each corner reflector34 could also be formed by three sheets joined together to form thethree planar surfaces 40 a, 40 b, 40 c.

Each corner reflector 34 extends towards the inside of the receiver 14.In other words, each corner reflector 34 extends on a side of thereceiver 14 comprising the photodiode 32. Thus, each corner reflector 34extends in the same direction as the direction of travel of thecollimated light beam 16.

In the example illustrated in FIG. 2, the convex surface 38 of thereceiver lens 30 and each corner reflector 34 extend on either side ofthe flat surface 36. However, in the example illustrated in FIG. 3, theconvex surface 38 of the receiver lens 30 and each corner reflector 34protrude from the same side of flat surface 36.

The receiver 14 can comprise a single corner reflector 34, or aplurality of corner reflectors 34. The plurality of corner reflectorsmay be arranged to form an array 44. By array, as shown in FIG. 6, it isto be understood that the plurality of corner reflectors 34 areregularly arranged. The plurality of corner reflectors 34 may form aline, a square or any other shape. The number of corner reflectors 34can be adapted to limit the size of the receiver 14 while stillsatisfactorily reflecting the collimated light beam 16.

In the example illustrated in FIGS. 4 and 5, the receiver 14 comprisestwo corner reflectors 34 a, 34 b aligned with each other. A first cornerreflector 34 a is adjacent to a second corner reflector 34 b. Here, asymmetry axis A₁ of the first corner reflector 34 a and a symmetry axisA₂ of the second corner reflector 34 b are equally distanced with theoptical axis X_(R) of the receiver lens 30.

The one or more corner reflectors 34 can be in one piece with thereceiver lens 30 to form a single optical part. The single optical partensures alignment of the optical axis X_(R) of the receiver lens 30 withthe symmetry axis A of each corner reflector 34. Alternatively, one ormore of the corner reflectors 34 may be separate parts. In such a case,the one or more corner reflectors 34 may be removed from the receiver 14after alignment is achieved, reducing the overall size of the receiver14.

The one or more corner reflectors 34 and the receiver lens 30 are bothmade out of an optically transparent material. The optical transparentmaterial may for example be a plastic, preferably polycarbonate,polymethyl methacrylate (PMMA) or a cyclo olefin polymer (COP), orglass.

In addition, the receiver 14 comprises an indicator (not illustrated)adapted to indicate whether the photoreceptor 32 is receiving thecollimated light beam 16. The indicator may for example be an LED, whichcan be switched on when the collimated light beam 16 is received. Thus,the indicator indicates when the optical axis X_(R) of the receiver lens30 is aligned with the optical axis X_(E) of the emitter lens 20. Theindicator may be used to adjust the position of the receiver 14 andovercome the spread of the collimated light beam 16 caused by the angleof divergence θ_(E). The reception of the collimated light beam 16 bythe receiver lens 30 may be improved.

The receiver lens 30, the photoreceptor 32, the one or more cornerreflectors 34 and electronic components used for powering, operation andcontrol of the receiver 14 are received in a second housing 46. Thesecond housing 46 may be fixed to a structural element to secureposition of the receiver 14.

In the illustrated example, the second housing 46 has a cylindricalshape. The optical axis X_(R) of the receiver lens 30 and the symmetryaxis A of each corner reflector 34 may be parallel to a longitudinalaxis of the second housing 46. Alternatively, the second housing 46could be rectangular or any other shape.

The second housing 46 is distinct from the first housing 28, so that theemitter 12 and the receiver 14 can be distanced from each other. Forexample, the emitter 12 and the receiver 14 may be placed over 50 mapart. Preferably, the emitter 12 and receiver are placed up to 15 mapart. A distance d separating the emitter 12 and the receiver 14overlaps the distance over which objects are to be detected by theoptical detection system 10.

Hereafter, a method 100 for achieving alignment between the emitter 12and the receiver 14 is described in more detail, with reference to FIGS.9a, 9b and 9c . According to method 100, alignment can be achievedwithout the operator needing to travel back and forth to iterativelyadjust the position of the emitter 12 and the receiver 14.

A first step 110, illustrated at FIG. 9a , comprises positioning theemitter 12 and the receiver 14 at the distance d. The distance dincludes the distance wherein objects are to be detected by the opticaldetection system 10. Preferably, the distance d is around or below 15 m.

A second step 120 comprises providing, by the emitter 12, the collimatedlight beam 16. The collimated light beam 16 is provided by switching onthe LED 18 of the emitter 12. The light from the LED 18 is collimated bythe emitter lens 20. The collimated light beam 16 travels towards thereceiver 14. However, the collimated light beam 16 diverges as ittravels towards the receiver 14 following the divergence angle θ_(E).The collimated light beam 16 spreads.

A third step 130 comprises adjusting the position of the emitter 12until the receiver 14 is within the radius r of the collimated lightbeam 16. The receiver 14 is within the radius r of the collimated lightbeam 16 when the reflected light beam 42 is observed at the emitter 12.As shown in FIG. 9b , the reflected collimated light beam 42 may beobserved even if the collimated light beam 16 is not parallel to theoptical axis X_(R) of the receiver lens 30. The reflected collimatedlight beam 42 may be observed by an operator or detected by thephotoreceptor 27 of the emitter 12.

Step 140, illustrated at FIG. 9c , consists in adjusting the position ofthe receiver 14 until the collimated light beam 16 is detected by thephotodiode 32 of the receiver 14 The detection of the collimated lightbeam 16 by the photodiode 32 indicates that the optical axis X_(E) ofthe emitter lens 20 is aligned with the optical axis X_(R) of thereceiver lens 30. Adjusting the position of the receiver 14 overcomesthe spread caused by the angle of divergence θ_(E) of the collimatedlight beam 16. The indicator (not illustrated) may indicate whether thecollimated light beam 16 is detected by the photoreceptor 32.

1. An optical detection system comprising: an emitter configured toprovide a collimated light beam; a receiver configured to receive thecollimated light beam, the receiver comprising: a receiver lens havingan optical axis, the receiver lens adapted to converge the collimatedlight beam along the optical axis, and at least one corner reflector,said at least one corner reflector comprising three planar surfacesperpendicular to each other and a symmetry axis coinciding with anintersection point of the three planar surfaces, said symmetry axisforming an equal angle with each of the planar surfaces, said at leastone corner reflector adapted to reflect the collimated light beam aboutthe symmetry axis, wherein the optical axis of the receiver lens isparallel to the symmetry axis of said at least one corner reflector. 2.The optical detection system according to claim 1, wherein the receiverlens and the at least one corner reflector are in one piece.
 3. Theoptical detection system according to claim 1, wherein the collimatedlight beam is within the visible spectrum or within the infraredspectrum.
 4. The optical detection system according to claim 1, whereinthe receiver comprises a plurality of corner reflectors forming anarray, and the array is preferably a line or a square.
 5. The opticaldetection system according to claim 1, wherein the receiver comprises afirst corner reflector and a second corner reflector aligned with thefirst corner reflector.
 6. The optical detection system according toclaim 1, wherein the collimated light beam converges at a focal point ofthe receiver lens, and the receiver comprises a photodiode positioned atthe focal point of the receiver lens.
 7. The optical detection systemaccording to claim 6, wherein the receiver further comprises anindicator configured to indicate whether collimated light is received bythe photodiode.
 8. The optical detection system according to claim 6,wherein said at least one corner reflector extend on a side of thereceiver comprising the photodiode.
 9. The optical detection systemaccording to claim 1, wherein the receiver lens and each cornerreflector are made of optically transparent material, preferably thereceiver lens and each corner reflector are made of polycarbonate,polymethyl methacrylate (PMMA), a cyclo olefin polymer (COP) or glass.10. The optical detection system according to claim 1, wherein theemitter comprises an LED and an emitter lens, and the LED is positionedat a focal point of the emitter lens to provide the collimated lightbeam.
 11. The optical detection system according to claim 10, whereinthe LED is pulse modulated.
 12. The optical detection system accordingto claim 1, wherein the emitter comprises a first housing and thereceiver comprises a second housing, distinct from the first housing.13. The optical detection system according to claim 1, wherein theemitter and the receiver are around 15 m apart.
 14. A method foraligning the optical detection system according to claim 1, wherein themethod comprises; providing, by the emitter, the collimated light beam;adjusting the position of the emitter to obtain a reflected collimatedlight beam at the emitter; and following adjustment of the emitter,adjusting the position of the receiver to align the collimated lightbeam with the optical axis of the receiver lens.